A friend's Ford Mondeo has served him well for 19 years and is now 22 years old. Recently the grarchsnges have become worrying erratic changing both up and down prematurely. I suggested changing the oil and filter in the autobox but he says it is sealed for life. I am dubious that life meant much over 10 years old and 100k! Do you think the oil and filter change are worth trying in case it is now s sludge box rather than a slush box?

Automatic transmission fluid condition depends very much how many heat cycles it's been through and how hot it got.

It's worth getting a sample of the fluid - on the end of the distick if it has one or briefly opening the fill/level plug - the colour will give a general indication of the fluid's condition - dull red is fine, brown could do with changing and black is too late!